Digital image data can be generated relative to various color spaces, e.g., standard Red Green Blue (sRGB) (standardized by International Electrotechnical Commission (IEC) 61966-2-1), National Television Standards Committee (NTSC), Phase Alteration Line (PAL), SEquential Color And Memory (SECAM), etc. But the color space of the source of the image data is very often not the color space of the output device (such as a monitor, printer, projector, etc.) that converts the image data into a visually perceptible analog thereof. In other words, where the source of the image data operates in a first color space and the output device operates in a second color space, it is usually desirable to convert the image data from the first color space to the second color space before outputting it via the output device.
Typically, the Background Art (such as in FIG. 1) has performed the color space (CS) conversion in the Central Processing Unit (CPU) of a computing device (such as a personal computer), not in the output device. FIG. 1 depicts a block diagram of a personal computer system according to the Background Art.
In FIG. 1, a personal computer (PC) 100 is depicted as including a CPU 102 and an output device 106 connected to the CPU 102 by signal path 114. FIG. 1 also depicts a source of image data 108 connected to the CPU 102 by the signal paths 110 and 112. The CPU 102 has a color space (CS) conversion module 104 that performs the function of converting image data from a first color space to a second color space. Thus, CS translation or conversion module 104 is depicted as the termination point for the signal paths 110 and 112. The output device 106 is depicted as taking the form of a monitor 106A that is a component of the PC or as a printer 106B that is external to the PC. Each of the monitor 106A and the printer 106B is considered external to the CPU 102.
In operation, the image data source 108 provides image data based in the first color space (CS1) and tag data representing parameters of the first color space via signal paths 110 and 112, respectively, to the CS conversion module 104 within the CPU 104 of the PC 102. Then, the CS conversion module 104 automatically converts the image data from the first color space to the second color space (CS2) according to the tag data for the first color space. And then the CS conversion module 104 outputs the image data based in the second color space to the output device 106 via the signal path 114.
It is noted that separate signal paths 110 and 112 for the image data and the associated tag data, respectively, have been depicted to emphasize that tag data is transferred to the CPU 102, while, in contrast, only CS2 image data is transferred out of the CPU 102 over the signal path 114. But it is not necessary that the image data and tag data be transmitted over two separate paths.
The CS conversion module 104 is typically implemented as software being run by the CPU 102. As such, the conversion speed of the software is limited by the system clock speed of the CPU 102. This raises the problem that the CPU, in general, cannot convert moving picture images (e.g., 100 million pixels per second) fast enough so that the moving pictures can be displayed on the output device (here, the monitor 106A) in real time.
The PC 100 of FIG. 1 has another problem. Suppose that it has to drive a second output device (not depicted), e.g., a liquid crystal display (LCD) projector, which is a typical requirement of a laptop PC. If the color space of the second output device is different than the color space (CS3) of the monitor 106A, the color conversion module 104 will attempt to convert the original image data from the source 108 into both CS2 image data and CS3 image data concurrently. For all but the smallest of image data sets, this represents a computational load that cannot be serviced in real time by the CS conversion module 104, i.e., the CPU 102. As a result, the monitor 106A and the second monitor cannot display the same image concurrently in real time.
As represented by a computer monitor (not depicted) marketed by the MITSUBISHI ELECTRIC CORPORATION (“Mitsubishi Denki”), Model No. LXA580W, it is known in the Background Art to locate non-automatic color space conversion functionality in an output device. Such a monitor includes a memory-containing conversion circuitry to convert input image data from one of a plurality of color spaces into the color space of the monitor.
A viewer/user of the Background Art monitor marketed by Mitsubishi Denki can manipulate a dedicated interface on the front of the monitor case to select one of the plurality of color spaces. Processing circuitry within the monitor accordingly will treat the input image data as if it has been generated within the selected color space. The processing circuitry will convert the input image data from the selected color space into the color space of the monitor. Then, the converted image data is displayed. The viewer/user views the displayed data to decide if its appearance is acceptable. Through trial and error, the conversion resulting in the best display appearance (according to the viewer's/user's personal preferences) can be selected.
The Background Art monitor marketed by Mitsubishi Denki has the advantage of providing enhanced quality of the displayed image. But it has the disadvantage that the user/viewer must actively participate in the optimization process each time data from a different color space is to be displayed.
In addition, where the image data displayed in a plurality of so-called windows relating to color spaces different from each other, parameters used for the color space conversion may be optimum for one of the windows, but not for other windows, and the resultant color reproduction may not be optimum for the above-mentioned other windows.
Furthermore, for user/viewers accustomed to color reproduction of domestic television sets, the color reproduction desired for the still picture is different from the color reproduction desired for moving pictures. For this reason, the user/viewer must actively participate in the optimization of the color reproduction each time there is a switching between the still pictures and the moving pictures.